The water-closet bowl comprises a bowl part in the form of a bowl for receiving and storing sewage therein and an inverted U-type trap discharge channel provided in communication with the bottom of the bowl. Further, on the upper, rear portion of the bowl part is provided a low tank for storing wash water supplied to the bowl part. The amount of water which enables the bowl part to be washed and, at the same time, sanitary sewage to be completely discharged by causing the siphoning action in the trap discharge channel is required. The required amount of wash water, which is different depending upon the size, shape and application purpose of the water-closet bowl, is usually approximately 13 liters each time the toilet is flushed.
Hereupon, saving the amount of wash water for a water-closet bowl has recently come to be demanded from the point of view of energy conservation. Moreover, making a low tank for storing wash water smaller in size and designing the position of installation of the low tank so as not to project as far upwardly as possible from the upper end of the bowl part as far as possible are demanded from the viewpoints of a smaller space for installation and a design.
As the construction for supplying wash water into the bowl part, a rim injection system is known in which a water path (rim water path) is formed within a rim part provided on the peripheral portion at the upper end of the bowl part, and a plurality of wash water injection holes are provided so that they communicate with the rim water path and the direction of the injected wash water is directed to the inner wall surface of the bowl part. Further, a so-called wash-down system is known in which, utilizing the head of water from the low tank, the wash water flows down from the low tank directly into the bowl part to flush the sewage therein. Also, a so-called siphon jet system is known in which wash water is spouted toward the inflow opening of the trap discharge channel provided at the bottom of the bowl part to produce the siphoning action in a short time.
The rim injection system has an advantage in that adjustment of the direction and diameter of the wash water injection hole enables the flow of the wash water in the bowl part to produce a turning force relatively easily, thereby permitting the sewage within the bowl part to be surely discharged while the inner wall of the bowl part is being washed. However, it has a disadvantage in that since the wash water is spouted from a number of injection holes provided along the rim part, the loss in energy is large before the jet of the wash water occurs and, therefore, the potential energy of the wash water stored in the low tank is not effectively be used. This makes the saving of the wash water in the case of the rim injection system difficult, and in the case where the amount of water is reduced, the position of installation of the low tank must be made higher.
In the wash-down system, since the wash water flows down from the low tank directly into the bowl part, the loss in energy is small and sewage can be discharged with a smaller amount of wash water. However, this system has disadvantages in that the sound produced when the wash water flows down is great and, because of the narrower surface of the accumulated water stored in the bowl part, it is easy for an offensive smell to occur and for sewage to stick to the inner surface of the bowl.
Further, while the siphon jet system has an advantage in that the noise at the time of washing is low, there is the problem of a large amount of wash water being necessary to sufficiently wash the interior of the bowl and completely discharge the sewage therein.
For this reason, an attempt has been made to combine the rim injection system and the siphon jet system to save the amount of wash water and to increase the washing effect (for example, JP-A Hei-2-194225, Japanese laid-open utility model publications Sho-63-91574 and Hei-3-62170).
However, in such a combined construction of the rim injection system and siphon jet system as known in the past, the water channel communicating with the rim water path and the water channel communicating with the jet water path originate from a common water channel, and such a common water channel branches off into the water paths on the way into the bowl, or the jet water path branches off from the rim water path. This results in many bent points of the water path and the longer jet water path, so that the wash water is made to produce a great loss in energy while it passes through the jet water path. Moreover, there is a problem in that the flow of the wash water contracts, is turbulent or the like at the positions where the water path branches, thereby also wasting the potential energy of the wash water in such positions.
Thus, with the conventional combined construction as mentioned above, it is difficult to make the low tank smaller in size and the position of installation thereof lower in height.